AC Apparatus & Devices

Brian Kim N. Benoza BSEE-4th year In the design of electrical power systems, the ANSI standard device numbers (ANSI /IEEE Standard C37.2 Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations ) identifies the features of a protective device such as a relay or circuit breaker. These types of devices protect electrical systems and components from damage when an unwanted event occurs, such as an electrical fault. Device numbers are used to identify the functions of devices shown on a schematic diagram. Function descriptions are given in the standard. One physical device may correspond to one function number, for example "29 Isolating Switch", or a single physical device may have many function numbers associated with it, such as a numerical protective relay. Suffix and prefix letters may be added to further specify the purpose and function of a device. ANSI/IEEE C37.2-2008 is one of a continuing series of revisions of the standard, which originated in 1928. ANSI Device Numbers Apparatus 

1 – Master Element

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2 – Time Delay Starting or Closing Relay

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3 – Checking or Interlocking Relay

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4 – Master Contactor

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5 – Stopping

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6 – Starting Circuit Breaker

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7 – Rate of Change Relay

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14 – Underspeed Device 15 – Speed – or Frequency, Matching Device

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16 – Data Communications Device

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17 – Shunting or Discharge Switch

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18 – Accelerating or Decelerating Device

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19 – Starting to Running Transition Contactor

8 – Control Power Disconnecting Device

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20 – Electrically Operated Valve

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9 – Reversing Device

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21 – Distance Relay

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10 – Unit Sequence Switch

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22 – Equalizer Circuit Breaker

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11 – Multi-function Device

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23 – Temperature Control Device

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12 – Overspeed Device

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24 – Volts Per Hertz Relay

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13 – Synchronous-speed Device

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25 – Synchronizing or SynchronismCheck Device

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26 – Apparatus Thermal Device

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27 – Undervoltage Relay

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46 – Reverse-phase or Phase-Balance Current Relay

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47 – Phase-Sequence or Phase-Balance Voltage Relay

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28 – Flame detector

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29 – Isolating Contactor or Switch

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30 – Annunciator Relay

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31 – Separate Excitation

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32 – Directional Power Relay or Reverse Power Relay

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33 – Position Switch

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34 – Master Sequence Device

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35 – Brush-Operating or Slip-Ring ShortCircuiting Device

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36 – Polarity or Polarizing Voltage Devices

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48 – Incomplete Sequence Relay 49 – Machine or Transformer, Thermal Relay 50 – Instantaneous Overcurrent Relay

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50G - Instantaneous Earth Over Current Relay (Neutral CT Method)

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50N - Instantaneous Earth Over Current Relay (Residual Method)

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50BF - Breaker failure

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51 – AC Inverse Time Overcurrent Relay

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51G- AC Inverse Time Earth Overcurrent Relay (Neutral CT Method)

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51N- AC Inverse Time Earth Overcurrent Relay (Residual Method)

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37 – Undercurrent or Underpower Relay

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38 – Bearing Protective Device

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39 – Mechanical Condition Monitor

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40 – Field (over/under excitation) Relay

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41 – Field Circuit Breaker

52a- AC Circuit Breaker Position (Contact Open when Breaker Open)

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42 – Running Circuit Breaker

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52b- AC Circuit Breaker Position (Contact Closed when Breaker Open)

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43 – Manual Transfer or Selector Device

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53 – Exciter or DC Generator Relay

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44 – Unit Sequence Starting Relay

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54 – Turning Gear Engaging Device

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45 – Abnormal Atmospheric Condition Monitor

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55 – Power Factor Relay

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56 – Field Application Relay

52 – AC Circuit Breaker

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57 – Short-Circuiting or Grounding Device

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58 – Rectification Failure Relay

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59 – Overvoltage Relay

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60 – Voltage or Current Balance Relay

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61 – Density Switch or Sensor

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62 – Time-Delay Stopping or Opening Relay

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77 – Telemetering Device

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78 – Phase-Angle Measuring Relay or "Out-of-Step" Relay

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79 – AC Reclosing Relay (Auto Reclosing)

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80 – Flow Switch

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81 – Frequency Relay

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82 – DC Reclosing Relay

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63 – Pressure Switch

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64 – Ground Detector Relay

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64R - Restricted earth fault

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64S - Stator earth fault

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65 – Governor

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86 – Lockout Relay/Master Trip

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66 – Notching or Jogging Device

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87 – Differential Protective Relay

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67 – AC Directional Overcurrent Relay

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88 – Auxiliary Motor or Motor Generator

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68 – Blocking Relay

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89 – Line Switch

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69 – Permissive Control Device

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90 – Regulating Device

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70 – Rheostat

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91 – Voltage Directional Relay

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71 – Liquid Level Switch

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92 – Voltage and Power Directional Relay

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72 – DC Circuit Breaker

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93 – Field Changing Contactor

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73 – Load-Resistor Contactor

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94 – Tripping or Trip-Free Relay

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74 – Alarm Relay

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96 – Busbar Trip Lockout relay

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75 – Position Changing Mechanism

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150 – Earth Fault Indicator

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76 – DC Overcurrent Relay

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83 – Automatic Selective Control or Transfer Relay 84 – Operating Mechanism 85 – Communications,Carrier or PilotWire Relay

ANSI Devices used in 5 MVA Transformers Fuses and switchgear E-rated power fuses are typically used in fused switches serving transformers. The purpose of the fuse is to allow for full use of the transformer and to protect the transformer and cables from faults. To accomplish this, the fuse curve should be to the right of the transformer inrush point and to the left of the cable damage curve. Typically, the fuse will cross the transformer damage curve in the long time region (overcurrent region). The secondary main device provides overcurrent protection for the circuit. “E” fuse ratings should always be greater than the transformer full load amps (FLA). The cable damage curve must be above the maximum fault current at 0.01 s. For transformers 3 MVA and less, standard overcurrent protection schemes for MV switchgear breakers should include an instantaneous and overcurrent combination relay (device 50/51). For transformers greater than 5 MVA, protection schemes become more complex. IEEE device numbers from IEEE C37.2 are used to outline the protection scheme. Transformer MV breakers may include the following protective device numbers: In MV systems, current transformers (CTs) connect protective or metering devices. CTs interface the electronic device and the MV primary system. The MV primary system voltage and current levels are dangerously high and cannot be connected directly to a relay or meter. The CTs provide isolation from the cable’s high voltage and current levels and translate the primary current to a signal level that can be handled by delicate relays/meters. The rated secondary current is commonly 5 amp, though lower currents such as or 1 amp are not uncommon. Protective relay’s CTs are expected to deliver about 5 amps or less under healthy load conditions. The current will go to a high value when a fault occurs. Per ANSI C57.13, normal protective CT class secondary should withstand up to 20 times for a short period of times under fault conditions. As a consequence, protective class CTs are accurate enough to drive a set of indication instruments, but will not be good enough for revenue class summation energy metering.